Explosive cartridge assemblies



March 11, 1969 s. F. FOSTER 3,431,848

EXPLOSIVE CARTRIDGE ASSEMBLI ES Filed April 28, 1967 Sheet of 2 23 FIG!FIG. 2

FIG.4

STEPHEN E STER IN NTOR.

AGENT March 11, 1969 s. F. FOSTER 3,431,348

EXPLOSIVE CARTRIDGE ASSEMBLIES Filed April 28, 1967 Sheet of 2 Z- 57 54STEPHEN E FOSTER INVENTOR. 62 I 5 e1 58 BY FIG. 8 PM AGENT United StatesPatent 3,431,848 EXPLOSIVE CARTRIDGE ASSEMBLIES Stephen F. Foster,Irving, Tex., assignor to Hercules Incorporated, Wilmington, Del., acorporation of Delaware Filed Apr. 28, 1967, Ser. No. 636,572

US. Cl. 10224 Claims Int. Cl. F42b 3/10 ABSTRACT OF THE DISCLOSURE Anexplosive cartridge assembly particularly adaptable for offshore seismicexploration is provided, of which the shell and at least one end closureis formed of plastic; a plurality of protruding ridge members aredisposed transversely on the shell outer wall to facilitate stacking;and each end closure, when plastic, is recessed centrally to provide aremaining peripheral rim portion to facilitate hand handling. Inpreferred practice the cartridge assembly contains a substantiallynoncompressible charge to facilitate stacking, and booster well and /orwall structure for self-disarming after a preset period of time in awater environment.

This invention relates to explosive cartridge assemblies particularlyadaptable for use in offshore seismic exploration. In one aspect thisinvention relates to explosive cartridge assemblies affording a maximumenergy loading per unit of cartridge gross weight. In another aspectthis invention relates to explosive cartridge assemblies that can bemore safely handled by hand than heretofore. In another aspect thisinvention relates to substantially cylindrical shaped explosivecartridges that can be stacked horizontally without incurring slippagealong the contacting surfaces with consequent failure of the stack. Inanother aspect, this invention relates to explosive cartridge assembliesfor offshore seismic exploration wherein the explosive is a rigid massand the individual cartridge assemblies can be stacked withoutencountering accidental breakage of the cartridge and/ or compressioneffects leading to distortion of shape of the stacked cartridges andaccompanying weakening of the stack. In still another aspect thisinvention relates to explosive cartridge assemblies, above described,which are self-disarming when misfired in a water environment and thereafter remaining uncontrolled in that environment. Other aspects of theinvention will be apparent to one skilled in the art in light of theaccompanying disclosure and the appended claims.

Explosive cartridge assemblies, particularly those utilized in offshoreseismic exploration, generally weigh from 25 to pounds, and although insome instances they have been formed from heavy fibrous materials, theyhave for the most part been formed from metal, not only to ensueprotection of the explosive against direct contact with water, but alsoto minimize breakage of the cartridge. However, the sharp edgesextending along the periphery at each end of the conventionally designedcartridge contribute to cuts and bruises of the hands and to the fingersof the operator during handling, and particularly to pinching of thefingers during stacking of the individual cartridge for storage. Suchinjuries to the hands and fingers have been incurred most frequentlyduring storage, transport and handling for offshore seismic explorationdue to the limited working space available for handling.

In offshore seismic exploration practice, the necessary mode oftransport of the cartridge assemblies to the shooting site is generallyby barge or boat. Working space is limited not only under thosetransport conditions but also during handling at the shooting site andit is therefore of special importance that the energy loading of eachcartridge, i.e. total amount of energy based on the gross weight of thecartridge, be as high as possible so as to afford a most efficientutilization of the available space. However, energy loading for metalcartridges utilized under these conditions has been unduly limited bythe weight of the metal components.

In the transport of cartridges, in offshore seismic prospecting, thepractice has been to stack the cartridge horizontally in piles ofmaximum allowable height in order to most efficiently utilize allavailable, though limited, space. Inasmuch as metal cartridges arenecessarily of limited wall thickness, their utilization in thispractice has often been disadvantageous due to damage imparted to theshell, including breakage, as a result of the excess weight of thestack, or pile. Also, in the stacking of metal cartridges under theabove-described storage and transport conditions, the weight of the pilehas often caused deformation of the cartridge with accompanyingcompression of the charge, which results in an increase in chargedensity and accompanying loss in sensitivity and/or a change of shape ofthe cartridge to impair its function as support for the pile, withaccompanying weakening of the pile contributing to its failure.

Further, it will be appreciated that the usual vessel for transport ofthese cartridge assemblies to the offshore seismic shooting site,whether a barge or other relatively small transport means, is of courselight in weight and undergoes extensive heaving action on the watersurface en route to the site. This has resulted in undue slippage of thestacked cartridges along their horizontal surfaces of contact withadjacent cartridges, which of course contributes to instability, andsometimes failure, of the pile and accompanying breakage and associatedhandling problems.

Explosive cartridges, when utilized in offshore areas, present apotential hazard when they fail to detonate, i.e. when they misfire,inasmuch as they are thereafter out of control, though still live. Thehazard is particularly serious when the misfired, but live, cartridge isultimately Washed ashore and then becomes a potential danger to thesafety of persons in that shore area.

This invention is concerned with watertight explosive cartridges,particularly adapted for offshore seismic exploration, which arefabricated from plastic, have improved energy loadings, can be readilystacked without slippage along the contacting cartridge surfaces, andcan be handled by hand without injury to the hands and the fingers ofthe operator. In preferred embodiments, the invention is concerned withsuch cartridges containing an explosive charge that is substantiallynoncompressible when the cartridge is stacked in piles of significantheight; and containing self-disarming structure to permit the cartridgeto become deactivated after misfiring in a water environment.

In accordance with the invention, an explosive cartridge assembly,particularly adaptable for offshore seismic exploration, is providedwhich comprises a substantially cylindrical plastic shell, a closuremember at each end of said shell in watertight closing relationshiptherewith and one said closure member containing an opening extendingtherethrough to the interior of said shell, and at least one of saidclosure members being formed from plastic; an explosive compositionwithin, and substantially filling, said shell; a well member within saidshell in operative contact with said explosive composition to supportinitiator means therefor, and supported in said shell at its open end inwatertight closing relationship with said opening; a plurality ofprotruding, and transversely extending ridge members on the outer wallof said shell;

and each said closure member, when plastic, containing a central portionthereof recessed into said shell so as to dispose the remainingperipheral portion as an outermost rim to facilitate hand gripping ofsaid shell.

In one embodiment of the invention, all except the booster well and oneend closure member of the uncharged cartridge assembly is plastic and isof an integral construction advantageously formed by blow molding. Theremaining end member is a metal closure and is crimped into closingposition after the charge is in place. The booster well is secured ineither of the end closure members as desired. The plastic closure memberis recessed along a central portion of its outside surface and has arounded, or convex, shaped external surface along its remainingperipheral rim portion.

In another embodiment, all but the booster well and a cover member foran opening in one end of the uncharged cartridge is of an integralplastic construction, also advantageously having been formed by blowmolding. Each plastic end closure member is recessed along the centralportion of its external surface and has a rounded or convex externalsurface along its remaining peripheral rim portion. The booster well issupported in either of the end members. The end member opposite thatsupporting the booster well contains the opening for charging theassembly and the cover member therefor placed in position after loadingis completed.

The transversely extending ridge members are preferably disposed in aplurality of spaced apart sets of at least two in each set. However, thetransversely extending ridges can be positioned in any suitable mannerso that when the cartridges are stacked horizontally they (the ridges)engage with corresponding ridge members of adjacent cartridges in theresulting pile to prevent lengthwise slippage of the cartridges alongcontacting surfaces.

The rounded, or convex, peripheral external surface of each plastic endclosure of the cartridge assemblies of the invention, eliminates hazardsin handling due to cutting and pinching of the hands and fingers of theoperator often incurred during handling in the crowded space that isavailable, particularly in offshore seismic work during loading andunloading of the barge, and handling at the shooting site for finalemplacement.

In a now preferred embodiment of the invention the explosive charge ofthe cartridge assembly is a formulation which when initially formed isreadily handled for charging the assembly but which subsequently sets toa rigid state, as described more fully hereinafter. This charge isutilized in preferred practice of the invention because, as a componentof a stacked cartridge, it undergoes substantially no compression inresponse to weight of the pile, and hence it can undergo no loss insensitivity when stacked, and it lends mechanical support to the plasticshell of the cartridge assembly, which is also of primary importancewhen the cartridge is stacked.

In other embodiments the invention utilizes, in combination, certainself-disarming members which, per se, are the inventions of others asdisclosed and claimed in the copending U.S. applications Ser. No.561,550 of Dittman et al., filed June 29, 1966, now Patent No.3,358,601, and Ser. No. 593,012 of Driscoll et al., filed Nov. 9, 1966,and also in the U.S. application of Hiram E. Driscoll, filedconcurrently herewith. The self-disarming features comprisewater-deteriorable members supported in the assembly, such as a discformed from a water-soluble, or water-disintegratable material supportedas a section in an end member of the cartridge assembly and in closingrelationship with the cartridge; and/or the booster Well formed fromsuch a water-soluble or water-disintegratable material. In any event,when there is a misfire of the cartridge in a water environment, i.e.failure to detonate, the disarming member, due to its resultingprolonged contact with the water, disintegrates or dissolves and thuspermits entry of water into the cartridge and ultimate washing ordissolving of the explosive charge from the shell to thereby render thecartridge harmless. This feature is particularly applicable in offshoreexploration areas wherein governmental authorities require thatprecaution be taken to avoid washing ashore of misfired, but live anduncontrolled, cartridge assemblies.

The invention is further illustrated with reference to the drawings ofwhich FIG. 1 is a view in cross-section of a substantially cylindricalcartridge assembly of which the shell and one end closure are plasticand the other end closure is metal, the booster well is supported in themetal end enclosure, the plastic end closure is shaped to facilitatehandling by hand, and a plurality of sets of transversely extendingridges are disposed on the exterior shell wall to prevent slippage ofthe cartridge when horizontally stacked with other cartridges havingsimilar ridge structure; FIG. 2 is the same as FIG. 1 except that bothend closures are plastic, and the end closure opposite the booster wellcontains an opening for charging the shell and a plastic cap, or cover,closure member closing the shell after charging; FIG. 3 is a view incross section, of a cap closure member, as an alternate form for thatshown in FIG. 2 and which contains, as a portion of the wall section, awater-soluble disc-shaped self-disarming member; FIG. 4 is anenlargement, for purpose of clarification, of a portion of the view ofFIG. 3; FIG. 5 is the same as FIG. 1 except that both end closuremembers are plastic, and the end closure, in place of the metal endclosure of FIG. 1, contains an opening for charging explosive into thecartridge and is closed by a bung-booster well assembly adapted to closethe opening after the cartridge is charged and to secure the boosterwell in operative position; FIG. 6 is the same as FIG. 2 except that theend closure, opposite that containing the booster well, is metal and thecartridge is charged through the open end prior to crimping the metalclosure member in place; and the metal end contains, optionally, awater-soluble or water-disintegratable self-disarming member; FIG. 7 isan enlarged and somewhat more detailed view of a now preferred means forsupport of a metal booster well in a plastic closure member of acartridge assembly of the invention; FIG. 8 is an enlarged and somewhatmore detailed view of a now preferred structure for support of a plasticbooster well in a plastic end closure member; and FIG. 9 is a detailedview of a now preferred structure for supporting a booster well in thebung structure of FIG. 5.

Referring to FIG. 1, elongated substantially cylindrical shell 10, endclosure member 11, and ridge member sets 12 and 13 of cartridge assembly9 are plastic and preferably of integral construction. End member 11contains a central recessed portion a along its outside surface, i.e.external to shell 10. The remaining external surface portion b of endmember 11, is a rim of convex or rounded contour about the periphery ofclosure 11.

Protruding ridge members of each of spaced apart sets 12 and 13 aretransversely disposed on the external surface of shell 10 and preferablyare each disposed in a plane substantially normal to the axis of shell10. Preferably, one of sets 12 and 13 is disposed near one of the shellend closures and the other is disposed near the opposite shell end.These ridge members, e.g., six ridge members of set 12 and three of set13 are disposed so as to engage with correspondingly positioned ridgemembers of other cartridges of the invention when they are stacked inhorizontal position.

Shell 10 is substantially filled with explosive charge 14 extendingfrom, and in contact with, end member 11, to the opposite end 16 ofshell 10. Charge 14 is preferably a rigid set type formulation describedmore fully herein, which is substantially noncompressible under theweight of the pile when cartridge 9 is stacked with other cartridges.Metal end closure member 17 of shell 10 is secured along its peripheryto shell end 16 by a crimp 17a. Metal booster well 18, e.g., bronze,copper, or aluminum, extends, closed end first, into shell 10 through acentral section of metal end member 17 and terminates in contact withexplosive charge 14, and it is supported at its open end in closuremember 17 by any suitable means. Well 18 is preferably supported withits open end flush, or nearly so, with the exterior surface of closure17. In one embodiment, a flange or rim extends peripherally along, andlaterally from, the outer wall of well 18 at its open end, and is seatedon metal end closure 17 outside shell 10, and soldered in its seatedposition to closure 17, to thereby support well 18 in closure member 17in watertight relationship therewith. Metal bale member 19 is secured toend closure 17 by engagement with metal lug members 21 which are securedin any suitable manner to the exterior surface of metal end closure 17.

A now preferred method for fabrication of assembly 9 of FIG. 1 comprisesthe steps of forming shell 10 including ridge members of sets 12 and 13and end closure 11 as an integral product of blow molding. The plasticis advantageously polyethylene preferably containing a filler toincrease its density to a value greater than that of sea water so as toenable the after-shot debris to sink after a successful firing and toenable the cartridge assembly to sink in the event of a misfiring. Theintegral plastic unit is then charged with explosive through the openend thereof (to be closed by metal end closure 17). Closure end 17, withbooster well 18 secured therein, is placed in position to close shell 10while at the same time supporting booster well 18 in operative contactwith explosive 14, and is then crimped to the end 16 of shell 10 tocomplete the closure of the assembly.

Referring to FIG. 2, shell 10, a booster well 18 and separate sets 12'and 13 of protruding ridge members transversely disposed around theshell 10', of cartridge assembly 9, and explosive charge 14' are thesame as those corresponding elements of cartridge assembly 9 of FIG. 1except that the transversely extending sets of ridges 12' and 13' aredisposed respectively at the ends of the cartridge opposite those ofFIG. 1. As illustrated the positioning of the ridges and the number ofridges in each set are optional, it being important that, in all events,the ridge members associated with one cartridge are positioned so as toengage correspondingly positioned ridge members of another of thecartridges of the invention when the cartridges are stackedhorizontally.

End closure members 23 and 24, sets 12 and 13 of the transverselyextending ridges, lugs 26, collar 27 and shell 10' of cartridge assembly9' are plastic and are preferably of integral construction,advantageously formed by blow molding. A central portion of end closure23 together with cap closure 28 therefor, as described below, formsrecess a along its external surface and extending into shell 10, and theremaining rounded peripheral portion b serves as a grip to facilitatehand handling of the cartridge.

End closure 24 of cartridge '9' contains an opening 25 extendingtherethrough. Collar 27, external to, and connecting in watertightrelationship with shell 10, encompasses opening 25 of end member 24.Booster well 18' extends, closed end first, through collar 27 andopening 25 of end member 24 and terminates in direct contact withexplosive charge 14' in shell 10'. Booster well 18' is supported incollar 27 at its open end in any suitable manner, preferablysubstantially flush with the top end 27 of collar 27. In one embodimentbooster well 18' when formed from a metal is flanged at its open end asdescribed with reference to well 18- of FIG. 1 and the flange, or rim,is seated in the end 27 of collar 27 and sealed thereto by suitableadhesive means. A now preferred support for a metal well 18 in collar 27is shown in FIG. 7. However, booster well 18' can be formed from plasticthe same as that forming collar 27 and then heat sealed in position incollar 27; or it can be formed from a plastic different from that ofcollar 27 and supported in collar 27 by a push nut in the mannerillustrated with reference to FIG. 8.

End closure 23 of cartridge assembly 9' contains an opening 29 through acentral portion thereof to permit charging of explosive into shell 10'.Thus with booster well 18' extending into shell 10', closed end first,in sealed relationship with end closure 24, explosive is charged throughopening 29 into shell 10' to substantially fill shell 10'. Plastic cover28, as a closure for opening 29, has a central portion 31 of itsexternal surface recessed and it is flanged along its periphery so as toengage opening 29 in closing relationship with shell 10'. Uponcompletion of charging the explosive into shell 10' through opening 29,cap closure 28 is suitably secured along the surface of its peripheralflange portion 31a to the external surface of the correspondinglyflanged periphery portion 31b of end member 23 forming opening 29, tothereby complete the assembly. Lugs 26, preferably forming an integralstructure with end member 24, are disposed within the recessed centralportion thereof, preferably spaced equally away from collar 27 tosupport bale 30 for carrying the cartridge assembly.

With reference to FIG. 3 is shown an alternate insert cover member 28'for cover member 28 of FIG. 2. Cover 28' is the same as cover 28 of FIG.2 except that it contains a water-deteriorable disc-shaped wall portion32 to provide for self-disarming of the cartridge in the event ofmisfire in a water environment. Thus, wall portion 32, after a presetperiod for normal firing of the cartridge when in a water environment,disintegrates in response to its contact with the water and permitsingress of water into the cartridge with consequent washing ordissolving of the explosive from the shell to disarm the shell of themain explosive charge. The embodiment of FIG. 3 is most advantageousapplied to the assembly 9' of FIG. 2 when booster well 18' is alsoformed from a water deteriorable member and the primary and secondaryinitiator means are self-disarming and/or self-desensitizing, asdisclosed and claimed in the above referred to US. application forpatent of Driscoll, filed concurrently herewith, to provide a resultingcartridge assembly which is self-disarming and/ or self-desensitizing inrespect of all its components after a misfire in a water environment.

FIG. 4 is a view of an enlarged portion of closure 28' of FIG. 3 andmore clearly illustrates water-deteriorable disc member 32 as a part ofthe closure cap 28'.

With reference to FIG. 5, cartridge assembly 9" is the same as assembly9 of FIG. 1 except that in lieu of the end closure member 17 of FIG. 1,and its directly associated elements, assembly 9" of FIG. 5 is closed byend closure member 33 which in turn contains opening 34 extendingtherethrough into shell 10" for charging explosive into shell 10", andbung-booster well assembly closure 36 for opening 34. Collar 37,attached to the external surface of shell end closure 33 in watertightrelationship therewith, encompasses opening 34. End closure member 11',shell 10", sets 12" and 13" of peripheral extending ridge members, endclosure 33, collar 37, and lug members 26' for support of bale 30, ofassembly 9", are plastic and preferably of integral construction.

End closure 33 of assembly 9" is recessed along a central portiond dthereof with the remaining peripheral portion e as a rim to facilitateease in hand handling. Peripheral rim e of end closure 33 has a convex,or rounded, contour along its surface external to shell 10" to minimizeinjuries to the hands and fingers of the operator during handling.

Bung-booster well assembly closure 36 for opening 34 in end closuremember 33, i.e. after charging shell 10", is a cover assemblycontaining, and supporting, booster well 18" at the open end of well18". Assembly 36 consists of bung 38 containing centrally disposedopening 39 extending therethrough and booster well 18" extending throughopening 39 closed end first and secured at its open end in bung 38 inwatertight relationship therewith. Bung booster well assembly closure 36in its watertight relationship with opening 34 supports booster well 18"in operative contact with explosive 14" in shell Lugs 26' support balemember 30 to facilitate hand carrying the cartridge.

Bung-booster well assembly closure 36 can be emplaced in closingrelationship with opening 34 in closure member 33 in any suitablemanner, a now preferred means being a lug-groove type structureillustrated with reference to FIG. 9.

Cartridge 9" can be assembled by charging the integral plastic unit,including shell 10", through opening 34 in end closure 33 and theninserting bung-booster well assembly closure 36 in place and twistlocking it in closing relationship with end member 33 as illustratedwith reference to FIG. 9.

With reference to FIG. 6, cartridge assembly 9" is the same as assembly9' of FIG. 2 except that in lieu of the end closure member 23 andassociated structure of FIG. 2, shell 10" is closed by metal closuremember 41 which is peripherally crimped to the bottom end 42 of shell10". Assembly 9" is charged through the open end of shell 10" to bethereafter closed by closure member 41.

Optionally, metal closure member 41 contains a waterdeteriorable element43 such as a water-soluble or waterdisintegratable plastic or awater-disintegratable fiber material, as a portion of the wall sectionthereof. Such a water-deteriorable material 43 is supported as a part ofthe wall of closure 41 in any suitable manner such as by a crimp of twoformed flanges along the periphery of an opening extending throughmember 41.

With reference to FIG. 7 is shown now preferred struc ture forsupporting a metal booster well in a plastic end closure of a cartridgeassembly of the invention. Thus, as shOWn in FIG. 7 plastic end closure44 contains opening 46 extending therethrough. Collar 47 is secured toend closure member 44 outside the cartridge shell and encompassesopening 46 in watertight closing relationship therewith. Booster well 48with peripheral flange 49 about its open end, and rolled bead 51disposed transversely about its outside wall in close proximity toflange 49, is supported at its open end in end closure 44, with flange49 seated on the end of collar 47 outside the cartridge shell, and withrolled bead 51 in tight contact with the inner wall of collar 47, tothereby provide a moisture seal and an internal lock to firmly securewell 44 in collar 47. Bulge 52 disposed transversely along the outsideof booster well 48, and extending laterally therefrom, is firmlypositioned against the inner wall 53 of end closure 44 to secure well 48in collar 44 in watertight relationship therewith.

In preferred practice, end closure 44 is blow molded as part of anintegral construction with the cartridge shell. Metal booster well 48,generally formed from copper, bronze or aluminum, is molded in positionas part of the blow molding process. Rolled bead 51, below flange 49,provides the interlocking action above described and in a final stepbooster well 48 is bulged to form bulge 52 at a point to provide acompressional load on the collar 47 and against the inner wall 53 of theend closure 44 to support the booster well 48 in position.

With reference to FIG. 8 is shown now preferred structure for supportinga plastic booster well in a plastic end closure of a cartridge assemblyof the invention. Thus, as shown in FIG. 8, plastic end closure 54contains opening 56 extending therethrough, and collar 57 is secured toend closure 54 outside the cartridge shell and encompasses opening 56 inwatertight closing relationship therewith. Booster well 58, withperipheral flange 59 about its open end, is supported at its open end inend closure 54 with flange 59 seated on the end of collar 57 outside thecartridge shell. Washer-like push nut 61 in engaging relationship withbooster well 58 immediately below the inner wall 62 of end closure 54 isadjusted by its forced contact with inner wall 62 to draw booster wall58 inwardly to thereby firmly secure flange 59 in its seated positionagainst the end of collar 57 to maintain the watertight relationship ofbooster 58 with collar 57.

FIG. 9 shows a now preferred means for securing a bung-booster wellassembly closure, such as assembly 33 of FIG. 5, in closing relationshipwith a plastic cartridge end closure therefor, such as end closure 33 ofFIG. 5. Thus, with reference to FIG. 9, a series of grooves 63 extendlongitudinally along the internal wall surface 64 of a collar 60attached to the plastic end closure of the cartridge, such as of collar37 attached to end closure member 33 of FIG. 5. Bung 66 containsprotruding lugs 67 laterally extending from its external side surfaces,and each lug 67 is spaced apart so as to engage one of the groovemembers 63, above described, so that when bung 66 is inserted intocollar member 60, it is guided in closing position therewith and withthe plastic end closure member of the cartridge. Booster well 68 can beeither plastic or metal and is supported in watertight relationship atits open end in bung 66 in any suitable manner such as illustrated withreference to FIG. 7 if booster well 68 is formed from a metal or asillustrated with reference to FIG. 8 if booster well 68 is formed from aplastic.

The length of the inner wall of the collar member 60 is correlated withthe length of the bung 66 so that when bung 66 is in closingrelationship with collar 60 lugs 67 extend just beyond the internal wallof the cartridge shell end closure but only so that when bung 66 in fullclosing position in the collar, is rotated, say, at about 45, each lug67 is moved along slightly inclined (toward the interior of thecartridge shell) path 65 on the inner wall of the cartridge end closureinto notch 69, in firm locked contact with the inner surface of theclosure member, in the respective notches 69, to thereby lock thebung-booster well assembly closure in its closing position.

Plastic cartridge assemblies of this invention can be fabricated fromany suitable plastic. A now preferred plastic material is a high densitppolyethylene, e.g. polyethylene filled to the amount of about 16 weightpercent with bleached barium sulfate of particle size less than 45microns, and which provides a polyethylene having a specific gravity inthe order of 1.07 grams per cc. as compared with 0.954 grams per cc.when unfilled. This increased density permits the cartridge to sink whenit would otherwise float uncontrolled in a water environment. It alsopermits fragments of the exploded cartridge to sink to thereby minimizelittering of the shoreline with washedashore cartridge fragments.

Any suitable explosive material can be utilized in the cartridgeassemblies of the invention, such as conventional dynamites,nitrocarbonitrates, and the like. Inorganic oxidizer salt explosives ofthe aqueous slurry type are often advantageously utilized. However, itis now preferred practice, and particularly in offshore seismicexploration, that a rigid set type formulation be utilized as discussedhereinabove. The preferred rigid type formulations arenitrocarbonitrates (NCNs) and can be prepared in accordance with any ofvarious suitable procedures known in the art. In one such preparativeprocedure about 1.5 weight percent water is admixed with the formulationat a temperature above about 110 F. and packaged at about thattemperature, or at a somewhat lower temperature level, if desired, say,as low as about 95 F. The packaged material becomes rigidly set when itreaches a temperature at or below the transition temperature of ammoniumnitrate which is about 86 F. Thus when the formulation is mixed at atemperature above, say, 95 F., it can be charged to the cartridge beforebecoming set and then permitted to set in the cartridge shell in formready for use as the explosive charge in an explosive cartridge assemblyof the invention.

Generally, the preferred rigid explosive charges of the cartridgeassemblies of the invention, prepared as above described with referenceto the transition temperature for ammonium nitrate, contain on a weightbasis from about 50 to percent ammonium nitrate; from 0 to 10 percentsodium nitrate, often from to percent; from 1 to 2 percent water,preferably about 1.5 percent; and the remainder, as sensitizer and fuelingredients, such as from 10 to percent aluminum, from 3 to 8 percentDNT oil or solid, and from 1 to 5 percent fuel oil. An exemplary rigidset NCN formulation, prepared as above described, is as follows:

Ingredient: Percent G-rained ammonium nitrate 76.0 Fuel oil 1.5Dinitrotoluene oil 5.0 Aluminum granules 16.0 H O 1.5

When a metal end closure is utilized in practice of the invention, theother closure member is formed from plastic and is recessed tofacilitate hand handling, as above described. In each instance of itsutilization, the metal end closure member is of conventional design forbeing crimped into closing relationship with the cartridge shell. By itsconventional design the metal end closure contains a recess on itsexternal surface, in close proximity to its periphery, to form aperipheral rim portion for crimping onto the cartridge shell. Althoughsuch a metal closure member utilized at both ends of the cartridge shellwould be unsuitable for accomplishing ease in handling in accordancewith the invention, one metal end closure in combination with a plasticend closure above described, is nevertheless advantageously utilizedinasmuch as once the operator has gripped the plastic end closure, heacquires improved hand control which, to a significant extent,compensates for the lesser degree of control normally effected byutilization of the metal end closure.

A metal end closure is most advantageously utilized, in practice of theinvention, when it is desired to load the cartridge through a completelyopen end of the cartridge shell. However, in preferred practice thecartridge assemblies of the invention contain the plastic closure memberat each end of the shell as illustrated with reference to the drawings,and hence to provide maximum protection against physical failure duringhandling, as well as to provide maximum ease in handling.

In preferred practice involving utilization of a metal end closure, theopen end of the plastc shell that is to accept the metal end closureterminates in a V which opens in a direction away from the shell; andthe lip of the metal end closure is roll crimped into the V end closure.This is of particular importance when the cartridge shell is maintainedat a minimum wall thickness to afford maximum energy loading, and isformed from blow moldmg.

Thus, when utilizing a densified polyethylene plastic, as abovedescribed, the shell wall thickness is often within the range of fromabout 50 to 80 mils. Accordingly, in such practice, the roll crimp ofthe metal end closure onto the cartridge shell, in combination with theV structure, above described, is necessary in order to provide therequired strength at the juncture of the cartridge shell and metal endclosure to compensate for loss in juncture strength that would havecharacterized a conventional crimp of the metal closure to the end ofthe thin plastic shell wall; for example, to impart strength to precludepopping off of the metal end of a stacked cartridge that often takesplace in response to weight of the pile when the metal end closure isconventionally crimped to the thin cartridge shell wall. The V portionis of integral construction with the cartridge shell, being readilyformed, for example, during blow molding of the particular plastic unit.

The individual protruding and transversel extending ridge members on theouter Wall of the cartridge shell can extend from the shell to anysuitable height, generally, most advantageously from about 0.03 to 0.10inch, more often in the order of about 0.05 inch.

The individual transverse ridge members around the cartridge shell,e.g., the sets 12 and 13, and of corresponding sets, of the drawings,can be disposed in any suitable pattern to facilitate stacking of thecartridge as above described. Also, the ridge members can advantageouslybe disposed in a coded pattern so as to indicate to the operator, by afinger touch of the patterned ridges, the end of the cartridgecontaining the booster well to thereby eliminate loss of time otherwiserequired for visual inspection of each cartridge to locate the boosterwell and determine the necessary handling for loading the booster unitinto the well. For example, a group of six ridges of set 12" of FIG. 6or a group of three ridges of set 13" of FIG. 5 can be standardized toform such a coded pattern, e.g., always being adjacent to the cartridgeend closure containing the booster well.

The invention also contemplates, as one embodiment, the above describedexplosive cartridge assembly, in combination with primary and secondaryinitiator means for the explosive charge to provide a complete assemblyready for firing. Such a complete assembly comprises the explosivecartridge assembly of the invention together with a booster assembly, asa secondary initiator, supported in the booster well and containing acap-sensitive booster charge such as PETN, tetryl, RDX, or the like, andan electric blasting cap or detonator fuse, as a primary initiator,supported in detonating relationship with the booster charge. Thebooster charge is detonated in response to initiation of the primaryinitiator, and the explosive charge is detonated in response todetonation of the booster charge to provide the full explosive force.

The plastic explosive cartridge assemblies of the invention areadvantageously applied to service in offshore areas, in lieu of metalcartridge assemblies, inasmuch as, under those conditions, they are notsubject to corrosive action of salt air and salt water during handlingand storage, whereas metal cartridges rapidly undergo external corrosionleading to physical failure of the cartridge shell there has been anopportunity for firing. Although metal assembly parts can be treated toresist corrosive action of salt water during handling and storage inoffshore areas, such treatment of an entire metal assembly is noteconomically feasible. Accordingly, shelf life of the plastic explosivecartridge assemblies of the invention, as regards corrosion resistanceduring storage and handling in offshore areas, is markedly superior tothat of explosive assemblies of conventional metal or fiber design.

The plastic cartridge assemblies of the invention are particularlyadvantageously utilized from the standpoint of fire hazard. Thus, ametal cartridge assembly, when exposed to heat in a fire area, undergoesinternal heat and pressure buildup and finally explodes to spew allcontents over the immediate area to thus create additional fire spread;and particularly so when the explosive charge contains aluminum. On theother hand, the plastic cartridge assembly of the invention, whenexposed to subheat conditions, simply melts to slump into a pile with nopressure-driven spewing of its contents.

Disarming members supported in the cartridge assembly, i.e. as a sectionin an end member of the cartridge and/or as booster well are formed fromany suitable water-deteriorable material exemplary of which arecarboxymethylcellulose (CMC), paper, poly(vinyl alcohol) and Klucel (ahydroxypropyl cellulose).

Such a water-deteriorable member, now preferred, is a hydroxypropylcellulose containing at least two and generally from 3 to 5hydroxypropyl groups per anhydroglucose unit. These hydroxypropylcellulose compounds are thermoplastic solids and are soluble in coldwater, insoluble in hot water, and are soluble in polar organicsolvents; and are disclosed and claimed in US. 3,278,521. They can beprepared in accordance with any suitable procedure such as disclosed andclaimed in US. 3,278,521 and US. 3,278,520. These compounds are readilymoldable as dis closed in US. 3,314,809.

When referring herein to self-disarming structure, it is generallycontemplated that during the preset time period there has been anunsuccessful attempt to fire the assembly, i.e. there has been amisfiring. However, in some instances of offshore operations, thecartridge assembly when placed in the water may become disassociatedfrom the firing energy source without any attempt having been made toactually fire it. In all events, in those embodiments of the inventioninvolving self-disarming structure, self-disarming takes place after thepreset time period for normal firing regardless of whether there hasbeen an unsuccessful attempt to actually fire the assembly.

A section of water deteriorable material in the cartridge shell end, orwall, employed in the embodiments providing self-disarming, having anarea equal to about that of a disc of from A to 1 inch in diameter isgenerally sufficient for admitting a self-disarming amount of water intothe cartridge shell after the preset period of time for normal firing;and if it is utilized in combination with a booster well also formedfrom a water-deteriorable material for self-disarming, as described, itssize can be correlated with the water deteriorability of the wellstructure as desired.

What I claim and desire to protect by Letters Patent 1. An explosivecartridge assembly for offshore seismic exploration comprising asubstantially cylindrical plastic shell; a closure member at each end ofsaid shell in watertight closing relationship therewith and one saidclosure member containing an opening extending therethrough to theinterior of said shell, and at least one of said closure members beingformed from plastic; an explosive composition within, and substantiallyfilling said shell; a booster well member within said shell in operativecontact with said explosive composition to support initiator meanstherefor and supported in said shell at its open end in watertightclosing relationship with said opening; means on said shell to preventlengthwise slippage of said assembly when it is stacked horizontallywith a like assembly, said means consisting of a plurality of ridgemembers disposed on the outer wall of said shell transverse to thelongitudinal axis of said shell and protruding from said wall so as tointerlock with corresponding ridge members of another said assembly whenstacked horizontally therewith; and each said end closure member whenplastic, containing a central portion thereof recessed into said shellso as to dispose the remaining peripheral portion of said closure memberas an outermost rim member having a rounded external surface.

2. An assembly of claim 1 wherein said plurality of ridges comprisesspaced apart Sets of ridges, and each said ridge is in a plansubstantially normal to the shell axis; and said shell, said ridgemembers, and each said closure member, when plastic, are of integralconstruction.

3. An assembly of claim 2 wherein said shell is closed at one end by ametal end closure member.

4. An assembly of claim 3 wherein said booster well is supported in saidmetal end closure.

5. An assembly of claim 3 wherein said booster well is supported in saidplastic end closure member.

6. In an assembly of claim 2, a plastic closure member in closingrelationship with said shell at each end thereof; the plastic endclosure member, opposite said booster well, containing an openingextending therethrough for loading said explosive into said shell; aplastic cap closure for the last said opening and said cap disposed inclosing relationship therewith.

7. An explosive assembly of claim 1 wherein said explosive compositionis a nitrocarbonitrate rigid set formulation and contains, on a weightbasis, from 50 to 80 percent ammonium nitrate, from to percent sodiumnitrate, from 1 to 2 percent water, and the remainder as fuel andsensitizer components, and prepared by mixing all ingredients at atemperature above the transition temperature of ammonium nitrate andsubsequently lowering the temperature of the admixture to below saidtransition temperature, whereby said explosive is a rigid solid.

8. In an explosive cartridge assembly of claim 6, the plastic closuremember for said shell opposite said cap closure member containing anopening extending substantially axially therethrough, and a plasticcollar attached to the outside surface of the last said end closuremember, in watertight relationship therewith and encompassing saidopening; and said booster well supported, at its open end, within saidcollar.

9. In an explosive assembly of claim 1, a plastic closure member inclosing relationship with said shell at each end thereof, and one saidclosure member containing an opening extending therethrough; a bungmember as a closure for the last said opening, and supported in closingrelationship therewith; and said booster well extending, closed endfirst, substantially axially through said bung, in watertightrelationship therewith, into said shell and terminating in directcontact with said explosive composition therein.

10. In an assembly of claim 1, said closure member, at the end of saidshell opposite said booster well, containing an opening extendingtherethrough into said shell; and a closure member for the last saidopening, in closing relationship therewith and water deteriorable aftera preset period of contact with water to then permit ingress of adisarming amount of water into said cartridge shell when said cartridgeis in contact with water for a period longer than said preset time.

11. An assembly of claim 10 wherein said waterdeteriorable member is awater-soluble plastic.

12. An assembly of claim 10 wherein said waterdeteriorable member is afibrous material.

13. An assembly of claim 1 wherein said booster well is formed from ahydroxypropyl cellulose containing at least two hydroxypropyl groups peranhydroglucose unit 14. An explosive cartridge assembly for offshoreseismic exploration, comprising a substantially cylindrical plasticshell; a plastic closure member at each end of said shell in watertightclosing relationship therewith; an explosive composition substantiallyfilling said shell; a booster well member extending through one of saidclosure members, closed end first, and in watertight relationshiptherewith, and terminating in direct contact with said explosive; meanson said shell to prevent lengthwise slippage of said assembly when it isstacked horizontally with a like assembly, said means consisting of aplurality of ridge members extending around the outer Wall of said shellin planes substantially normal to the longitudinal axis of said shell,and protruding from said wall so as to interlock with correspondingridge members of another said assembly when stacked horizontallytherewith as described; each said plastic end closure containing acentral portion thereof recessed into the said shell so as to disposethe remaining peripheral portion of said closure member as an outermostrim having a rounded external surface; the plastic end closure memberopposite said booster well containing an opening extending therethroughinto said shell for charging said explosive into said shell; and aplastic cover member for closing said opening, and in watertight closingrelationship therewith.

15. In an explosive assembly of claim 14, said plastic cover membercontaining an opening extending therethrough into said cartridge shell,and a water-deteriorable material as a closure for the last said openingin closing relationship therewith, and deteriorable after a presetperiod of contact time for water to permit ingress of water into saidcartridge shell when said shell remains in contact with water for aperiod longer than said preset time.

16. An assembly of claim 15 wherein said water-deteriorable material isa hydroxypropyl cellulose containing from 2 to 10 hydroxypropyl groupsper anhydroglucose unit.

17. An assembly of claim 16 wherein said booster well member is alsoformed from a hydroxypropyl cellulose containing from 2 tohyd-roxypropyl groups per anhydroglucose unit.

18. An assembly of claim wherein each said plastic end closure, saidcartridge shell and said ridge members constitute an integralconstruction of densified polyethylene.

19. An assembly of claim 18 wherein each of said ridge members extendsfrom said shell at a height in the range of from 0.03 to 0.10 inch.

20. An explosive cartridge assembly for offshore seismic exploration,comprising a substantially cylindrical plastic shell; a plastic closuremember at one end of said shell, and a metal end closure member at theopposite end of said shell, each said end closure member being disposedin watertight closing relationship with said shell; an explosivecomposition substantially filling said shell; a booster Well memberextending through said plastic end closure member, closed end first, andin Watertight relationship with said plastic closure member andterminating in direct contact with said explosive; means on said shellto prevent lengthwise slippage of said assembly when it is stackedhorizontally with a like assembly, said means consisting of a pluralityof ridge members extending around the outer Wall of said shell in planessubstantially normal to the longitudinal axis of said shell; andprotruding from said wall so as to interlock with corresponding ridgemembers of another said assembly when stacked horizontally therewith asdescribed; said plastic end closure containing a central portion thereofrecessed into said shell so as to dispose the remaining peripheralportion as an outermost rim member having a rounded external surface;said metal end closure being supported in its closing relationship withsaid shell by a rolled crimp, and containing an opening extendingtherethrough into said shell; and a fiber closure member as a closurefor the last said opening and supported in closing relationshiptherewith, and water deteriorable after a preset period of contact withwater to then permit ingress of a disarming amount of water into saidcartridge shell when said cartridge is in contact with water for aperiod longer than said preset time.

21. An explosive assembly of claim 1 wherein said plastic is a densifiedpolyethylene.

22. An explosive assembly of the claim 21 wherein said polyethylenecontains bleached barium sulfate of particle size less than aboutmicrons as a densifying agent therefor.

23. An explosive assembly of claim 22 wherein the Wall thickness of saidcartridge shell is in the range of from to mils.

24. An explosive assembly of claim 23 wherein each of said ridge membersextends from said shell at a height in the range of from 0.03 to 0.10inch.

25. In an assembly of claim 1, initiator means for said explosivecomposition, supported within said booster well.

References Cited UNITED STATES PATENTS 2,953,093 9/1960 Chase et a1.102-24 3,186,340 6/1965 Foster 102-24 3,254,601 6/1966 Grifiith et al10224 3,306,200 2/1967 Branscum et al. l0224 3,322,066 5/1967 Griflithet al 10224 3,358,601 12/1967 Dittmann et al l0228 VERLIN R. PENDEGRASS,Primary Examiner.

